1. Field of the Invention
The present invention generally relates to a transfer assembly used in an electronographic tandem image forming apparatus including a laser printer, an LED (light-emitting diode) printer, a facsimile machine, etc., and an electronographic tandem image forming apparatus including the transfer assembly.
2. Discussion of the Background
In recent years, tandem image forming apparatuses have attracted attention as color image forming apparatuses because there is a need to output full color images as fast as a speed with which monochrome images are output.
Tandem image forming apparatuses include a plurality of photoreceptors and a transfer assembly including a plurality of transferers and an intermediate transfer belt or a transfer and transport belt. A different color image is formed on each of the photoreceptors. Two method are used to transfer images on the photoreceptors, a direct transfer belt method and an intermediate transfer belt method.
In the direct transfer belt method, the images are transferred sequentially by transferers and superimposed one on another directly onto a recording medium that is transported by a transfer and transport belt. In the intermediate transfer method, the images are transferred sequentially by transferees and superimposed one on another on an intermediate transfer belt, and then the superimposed image is transferred by a secondary transferee onto the recording medium. In both methods, the transferees in the transfer assembly are facing one of the photoreceptors via the transfer and transport belt or the intermediate transfer belt.
Although transferees typically include a conductive rubber or a conductive sponge material, which deteriorates over time, compatibility thereof is rarely considered because useful life thereof is longer than that of the intermediate transfer belt or the transfer and transport belt included in the transfer assembly together with the transferees.
Further, when a transferer including a conductive rubber or a conductive sponge material is touched by hand during maintenance work, the transferer may be stained, deformed, or damaged. Although an axis of the transferee can be touched, the axis is typically unexposed.
Image forming apparatuses typically manage the useful life of the transfer assembly based on usage history thereof, such as the number of sheets printed, and do not manage the useful life of the transferees included therein individually.
In a related-art image forming apparatus, transfer rollers are held in sub-frames in a transfer belt assembly as shown in FIG. 1. In FIG. 1, a transfer belt assembly 300 includes a transfer belt 301 stretched around a driving roller 310 to rotate the transfer belt 301, a tension roller 320 to apply tension to the transfer belt 301, and driven rollers 330 and 340. The transfer belt assembly 300 further includes a black sub-frame 350, in which a transfer roller 370 for black is attached, and a full-color sub-frame 360, in which three transfer rollers 370 are attached. In both the black sub-frame 350 and the full-color sub-frame 360, each transfer roller 370 is located at a position to contact a photoreceptor drum, not shown, via the transfer belt 301. Each transfer roller 370 is provided with a bearing 380 and pressed against the transfer belt 301 by a spring 390.
The black sub-frame 350 and the full-color sub-frame 360 are for simplifying engagement and disengagement of the transfer rollers 370 with/from the transfer belt 300. More specifically, in monochrome printing, the three transfer rollers 370 held in the full-color sub-frame 360 are disengaged from the transfer belt 301 altogether by an action of the full-color sub-frame 360 because these transfer rollers 370 are not used. In color printing, all three transfer rollers 370 engage the transfer belt 301 by an action of the full-color sub-frame 360.
However, in the configuration described above, replacing individual transfer roller 370 is not easy. For example, when one of the three transfer rollers 370 held in the full-color sub-frame 360 is to be replaced at the end of its useful life, it is necessary to remove the bearing 380 and the spring 390. To save trouble removing the bearing 380 and the spring 390, the full-color sub-frame 360 should be replaced with a new one, thus wasting the other two transfer rollers 370 that are still useful.